Light and GABA Receptor Activation Change Daily Gene Levels in the Brain’s Internal Clock of Day-Active Nile Grass Rats

Per1 mRNA was highest in the early to mid-subjective day, while Per2 mRNA levels peaked in the late subjective day.

• Per1 and Per2 mRNA levels vary rhythmically in the suprachiasmatic nucleus over a circadian cycle in constant darkness.
• Acute light exposure in the early subjective night significantly increases both Per1 and Per2 mRNA levels.
• Injection of the GABA(A) receptor agonist muscimol into the SCN during the subjective day decreases Per2 mRNA levels 1 and 2 hours post-injection, but does not affect Per1 levels.
• Muscimol reduces light-induced Per2 mRNA in the early subjective night, while the induction of Per1 by light remains unaffected.
• Phase shifts induced by muscimol during the daytime are associated with significant decreases in Per2 mRNA, suggesting a potential mechanism for phase delays in diurnal animals.

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